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73 lines
2.6 KiB
Markdown
73 lines
2.6 KiB
Markdown
# Introduction
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Deno is a JavaScript/TypeScript runtime with secure defaults and a great
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developer experience.
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It's built on V8, Rust, and Tokio.
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## Feature highlights
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- Secure by default. No file, network, or environment access (unless explicitly
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enabled).
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- Supports TypeScript out of the box.
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- Ships a single executable (`deno`).
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- Has built-in utilities like a dependency inspector (`deno info`) and a code
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formatter (`deno fmt`).
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- Has
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[a set of reviewed (audited) standard
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modules](https://github.com/denoland/deno_std) that are guaranteed to work
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with Deno.
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- Scripts can be bundled into a single JavaScript file.
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## Philosophy
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Deno aims to be a productive and secure scripting environment for the modern
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programmer.
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Deno will always be distributed as a single executable. Given a URL to a Deno
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program, it is runnable with nothing more than
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[the ~15 megabyte zipped executable](https://github.com/denoland/deno/releases).
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Deno explicitly takes on the role of both runtime and package manager. It uses a
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standard browser-compatible protocol for loading modules: URLs.
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Among other things, Deno is a great replacement for utility scripts that may
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have been historically written with Bash or Python.
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## Goals
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- Only ship a single executable (`deno`).
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- Provide secure defaults.
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- Unless specifically allowed, scripts can't access files, the environment, or
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the network.
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- Be browser-compatible.
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- The subset of Deno programs which are written completely in JavaScript and
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do not use the global `Deno` namespace (or feature test for it), ought to
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also be able to be run in a modern web browser without change.
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- Provide built-in tooling to improve developer experience.
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- E.g. unit testing, code formatting, and linting.
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- Not leak V8 concepts into user land.
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- Serve HTTP efficiently.
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## Comparison to Node.js
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- Deno does not use `npm`.
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- It uses modules referenced as URLs or file paths.
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- Deno does not use `package.json` in its module resolution algorithm.
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- All async actions in Deno return a promise. Thus Deno provides different APIs
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than Node.
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- Deno requires explicit permissions for file, network, and environment access.
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- Deno always dies on uncaught errors.
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- Uses "ES Modules" and does not support `require()`. Third party modules are
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imported via URLs:
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```javascript
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import * as log from "https://deno.land/std@$STD_VERSION/log/mod.ts";
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```
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## Other key behaviors
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- Remote code is fetched and cached on first execution, and never updated until
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the code is run with the `--reload` flag. (So, this will still work on an
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airplane.)
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- Modules/files loaded from remote URLs are intended to be immutable and
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cacheable.
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